1. Field of the Invention
This invention relates to a linear drive mechanism for use in an optical disk device, and more particularly a method for controlling a linear motor to move an objective lens for providing a beam waist of an optical beam to a recording surface of the optical disk and extracting a light beam reflected by the recording surface of the optical disk along the recording surface.
2. Description of the Related Art
Generally, an optical disk device includes an optical head, a linear moving mechanism, a position controlling section, a loading mechanism, a disk driving section, and a signal controlling section. The optical head is used to focus a laser beam onto an optical disk to write data to the optical disk and read from the optical disk. The linear moving mechanism is used to roughly move the optical head along a recording surface of the optical disk. The position controlling section is used to control the optical head and the linear moving mechanism. The loading mechanism is used to guide the optical disk to a predetermined position. The disk driving section is used to rotate the optical disk at a predetermined speed. The signal controlling section is used to read data recorded in the optical disk and store data in the optical disk.
The optical head has a laser device, a light transmission member, an objective lens, a photodetector, a lens holder, a focusing mechanism, and a tracking mechanism.
The laser device generates a laser beam, which is used to write data to the optical disk and to read data from the optical disk. The light transmission member guides the laser beam from the laser device, and separates the laser beam reflected by the optical disk from the laser beam directing to the optical disk from the laser device. The objective lens is used to focus the laser beam from the laser device onto the surface of the optical disk by a predetermined beam spot size, and to receive the laser beam reflected by the optical disk to be restored to a predetermined beam spot size. The photodetector detects the laser beam picked up by the objective lens to be converted to an electrical signal. The lens holder holds the objective lens to be movable in an arbitrary direction. The focusing mechanism is used to move the lens holder with the objective lens to a direction perpendicular to the recording surface of the optical disk, that is, focus direction in accordance with an output from the photodetector, so that the laser beam, which is sent from the laser device and passed through the objective lens, is correctly focused on a predetermined position of the optical disk. The tracking mechanism is used to move the lens holder, that is, the objective lens in a direction, which is parallel to the recording surface of the optical disk and perpendicular to the track, in accordance with the output from the photodetector, so that a center of the laser beam, which is sent from the laser device and passed through the objective lens, is conformed to a center of the track formed in the recording surface of the optical disk.
The linear moving mechanism has a base member, a guide rail, a support member, a moving coil, and a magnetic circuit.
The base member supports the optical head to be movable along the surface of the optical disk. The guide rail guides the base member. The support member is provided between the base member and the guide rail to reduce an axial addition between the base member and the guide rail. The moving coil generates magnetic force for moving the optical head along the guide rail. The magnetic circuit provides magnetic flux for converting magnetic force generated by the moving coil to driving force. In order to reduce the manufacturing cost of the optical disk device, there has been recently used a solid bearing of reasonable cost, for example, oil impregnation bush.
In this type of the optical disk device, the optical disk is guided to a predetermined position by the loading mechanism, and the optical disk is rotated at a predetermined speed by the disk driving section. Then, a laser beam having a predetermined light density is generated from the laser device by the control of the signal controlling section. A distance between the objective lens and the recording surface of the optical disk is focus-locked to a fixed value based on the laser beam. Under this state, a predetermined current is supplied to the moving coil of the linear moving mechanism by the tracking control of the position controlling section. Thereby, the objective lens, that is, lens holder is moved and the center of the laser beam passed through the objective lens is conformed to the center of the track, and the center of the laser beam passed through the objective lens is conformed to the track of the innermost periphery of the optical disk.
Thereafter, a predetermined current is supplied to the moving coil of the linear moving mechanism from the position controlling section, so that the optical head, that is, the objective lens is roughly moved in the vicinity of a target track directed by the signal controlling section. Sequentially, the center of the target track and the center of the laser beam passed through the objective lens are slightly moved to be conformed to each other by a track jump of the tracking mechanism of the lens holder.
Header data of the optical disk is checked by the signal control section based on the reflected light from the track moved by the close access, that is, the track jump. Then, when the target track directed by the signal controlling section and the track moved by the jump are conformed to each other, data is written to the target track or read from the target track.
As mentioned above, in the optical disk device, which has been recently used, the optical head is moved by the linear moving mechanism, and the objective lens is moved by the tracking mechanism. In other words, the objective lens is moved to the target track by two moving mechanisms, that is, linear moving mechanism, and the tracking mechanism. Therefore, there are problems in the point that the cost of parts, which are necessary to provide the optical head access mechanism, and the cost of assembling the optical disk device are increased.
There has been tried that the tracking mechanism of the objective lens is omitted and the tracking is controlled by only the linear moving mechanism. However, in many cases, since friction (axial thrust load) between the guide rail of the linear moving mechanism and the support member is large, it is substantially difficult to newly move the objective lens (optical head), which is moved in the vicinity of the target track, by an amount corresponding to several tracks.
As a method for reducing friction (axial addition), there has been proposed an example using a high accurate bearing, serving as a support member, in which friction between the support member and the guide rail is sufficiently reduced. However, the high accurate bearing is extremely expensive, and there is generated a problem in which the manufacturing cost of the optical disk device is more increased if such a high accurate bearing is used.